JPH0562167A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium which can be used especially for a digital VTR or a large-capacity floppy disk, etc., for a high-performance magnetic recording medium which enables an electromagnetic conversion characteristic at a high recording density region to be improved. CONSTITUTION:A magnetic paint 4 is applied on a non-magnetic base film 3 from a nozzle 1 for forming pre-coating a magnetic layer 5, a post-coating magnetic layer 6 is applied by a nozzle 2, and a backing layer is formed, thus enabling a magnetic recording medium to be constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-performance magnetic recording medium capable of improving electromagnetic conversion characteristics in a high recording density area, and particularly used for a digital recording tape or a large capacity floppy disk. The present invention relates to a possible magnetic recording medium and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, in the magnetic recording field, a magnetic coating material containing a ferromagnetic powder and a resin binder is dispersed and coated on a non-magnetic base film such as polyethylene terephthalate (PET), that is, a coating type magnetic recording medium is the most widely used. Has been used. A magnetic recording medium for recording and reproducing needs various characteristics to improve it.

For example, in the case of a magnetic tape for VTR, many signals such as a luminance signal, a color signal, a linear audio signal, an FM audio signal and a control signal are recorded. In the case of a home VTR, the luminance signal, the color signal and the FM audio signal are superimposed on the same track. The luminance signal has a relatively short recording wavelength of about 1 μm and is directly recorded by FM, so that it is recorded on the extreme surface layer portion of the magnetic layer. It is conventionally known that a color signal has a long recording wavelength and is recorded even in the deep part of the magnetic layer.

Among the domestic VTRs, in the case of the VHS system,
Since the video signal is overwritten after the FM audio signal is recorded by a dedicated wide gap head, the recorded part is erased and only the residual component remains as a signal. Conventionally, improvement of tape characteristics has been achieved by increasing the Hc, increasing the packing rate of magnetic powder particles, and super smoothing the surface of the magnetic tape. However, the improvement of the image output due to the high Hc of the magnetic tape causes a decrease in the output at the low frequency corresponding to the color signal area, and when the magnetic tape is comprehensively viewed, it becomes an unbalanced tape. Also, high H
Since there is an increase in the recording current due to the conversion to c, there remains a problem in compatibility.

Further, current magnetic recording generally uses a method of using in-plane magnetization of a recording medium. But,
In the recording method using the in-plane magnetization, if an attempt is made to increase the recording density, it is difficult to obtain a high recording density above a certain level because the demagnetizing field in the recording medium increases. In order to exceed such a limit of recording density, a perpendicular magnetic recording method using magnetization in a direction perpendicular to the surface of a recording medium has been proposed in recent years.

This perpendicular magnetic recording system has a characteristic that the demagnetizing field in the recording medium is reduced at high recording density.
It can be said that the recording method is essentially suitable for high density recording.

The recording medium used in the perpendicular magnetic recording system is
There are continuous films such as Co—Cr vapor deposition films and coating films in which hexagonal plate-shaped barium ferrite fine particles are dispersed in a resin. In particular, recently, a coated film type perpendicular magnetic recording medium has been drawing attention from the viewpoints of cost advantages of the coating type and practicality such as durability. In the case of a coated film type perpendicular magnetic recording medium, the plate-like particles have an axis of easy magnetization in a direction perpendicular to the plate surface, and the easy axis of magnetization is easily oriented in the direction perpendicular to the substrate surface during coating. On the other hand, barium ferrite magnetic powder suitable for high density recording has a plate-like shape and is ultrafine particles.
Since the plate thickness is 100 to 1000 angstrom, it has a potential as a longitudinal orientation medium.

The VTR tape has a high output from a low frequency range to a medium and short wavelength range and is composed of a multi-layer magnetic layer having abundant luminance signal, color signal and audio signal characteristics.
R tape has been developed and is already on the market. On the other hand, there is a movement to actively apply barium ferrite to tape applications, and it is considered to use it by taking advantage of the high recording density characteristic of barium ferrite. In the field of floppy disks, 2 ED with a capacity of 4 MB has finally begun to be put on the market, and the trend toward smaller size and larger capacity is rushing.

[0009]

However, in the current development of the coating type magnetic recording medium, the high Hc and magnetic properties which have been made to further improve the characteristics of the recording medium as disclosed in the prior art. For high density packing of powder, super smoothing of magnetic tape surface, stacking of different magnetic layers, etc.
Problems such as unbalanced tape, deviation from compatibility due to increase in recording current, securing running durability by increasing the filling rate of magnetic powder, and causing a slackening phenomenon in mid-range characteristics was there. Further, in order to improve the recording density, it is effective to produce a medium in which barium ferrite magnetic powder having a plate-like shape and having uniaxial anisotropy is vertically aligned.
On the other hand, it cannot be denied that the output in the long wavelength region is smaller than that in the longitudinal recording medium.

That is, the tape of the conventional longitudinal recording medium is used.
There is no almighty magnetic tape that satisfies compatibility while improving compatibility. On the other hand, in a floppy disk using barium ferrite magnetic powder, a medium with excellent frequency characteristics has been obtained by orienting highly vertically, but waveform distortion causes a problem that requires correction processing such as waveform equalization on the circuit. Accompany. Further, when used as a coating type medium using barium ferrite magnetic powder, especially for tape, the surface property of the tape obtained is that the properties of the magnetic coating containing barium ferrite magnetic powder are completely different from those of conventional magnetic coatings. Is a conventional commercial SVHS tape or 8 mm
Problem that the good electromagnetic conversion characteristics expected from the beginning cannot be obtained because it is far inferior to the tape surface property that has been achieved by the coating type tape such as the metal tape for H8 and Hi8. was there.

[0011]

A magnetic recording medium of the present invention,
In order to solve the above-mentioned problems, a non-magnetic base is manufactured by using two coating nozzles separately provided with a magnetic coating material containing a hexagonal ferrite plate-like magnetic powder and a resin binder in a wet state. It is characterized by simultaneous multi-layer coating on a film, that is, a composition in which a magnetic coating material having the same properties is simultaneously multi-layer coated in a wet state,
In order to enable simultaneous superposition of magnetic paints of the same nature, two single nozzle die nozzle coaters having a fixed curvature or a single double nozzle die nozzle coater is installed. When the obtained magnetic layer is in the form of a tape, it is preferable to impart anisotropy in the in-plane longitudinal direction, but the present invention is not limited to this. More preferably, the easy axis of magnetization is set in the medium thickness direction. It is desirable to configure it to have.

[0012]

The present invention has the above-mentioned structure,
Achievement of medium surface properties that could not be obtained with conventional coating type media using hexagonal ferrite magnetic powder, recording density characteristics superior to conventional longitudinal longitudinal recording media, and conventional barium ferrite single layer The recording sensitivity exceeds that of tape. This is a pre-coating method in which plate-shaped particles of hexagonal ferrite magnetic powder are arranged in the longitudinal direction of the medium in a magnetic recording medium having a multilayer structure using hexagonal ferrite magnetic powder as in the present invention and having the same paint properties. By providing the layer, the fluidity of the coating of the layer containing the hexagonal ferrite magnetic powder forming the final surface is improved and the surface smoothing is promoted.

As a result, the first coating layer acts as a shock absorber, and the hexagonal ferrite magnetic layer of the second coating layer is smoothed. At this time, it is preferable that the resin binder used for the magnetic paint has a low Tg. Even if the magnetic recording medium having the same paint properties is applied twice, it does not change from the case of a single layer magnetic recording medium, and the surface property of the medium is further improved. This allows
As a result of higher performance, it is possible to supply a magnetic recording medium that has improved output, reduced noise, and improved recording sensitivity in the recording frequency range used.

[0014]

EXAMPLE An example of the magnetic recording medium of the present invention and a method of manufacturing the same will be described below.

Example 1 First, the following materials were used as the pre-coated magnetic layer to form a coating. Barium ferrite ----- 100 parts by weight Vinyl chloride resin ---------- 9 parts by weight Polyurethane resin ----- 7 parts by weight α-alumina ---------- 7 parts by weight Stearic acid ------------- 3 parts by weight Carbon black -------- 1 part by weight MIBK ----------- 96 parts by weight Toluene ------------- Parts by weight Cyclohexanone ------ 48 parts by weight After mixing the above materials, they were dispersed for a certain period of time with a kneader, a mixer and a sand mill. The grain size of the barium ferrite used was 0.05 μm, the plate ratio was 3, and the coercive force was 895O.
The one of e was used. As the post-coating magnetic paint, the same format was used except that the amount of α-alumina used in the above-mentioned pre-coating magnetic paint was 3 parts by weight and the particle size was 0.1 μm, and the paint viscosity was set to 5 poise lower.

The obtained magnetic paint was applied to two non-magnetic support films, here 10 μm, by two single-die die nozzle coaters arranged at intervals as shown in FIG.
It was applied to a m-thick polyethylene terephthalate film so as to have a film thickness of 2.5 μm, and was passed through an orienting device that generates a magnetic field in the same direction as the supporting film running direction to orient in the medium longitudinal direction.

In FIG. 1, 1 is a nozzle for coating a magnetic layer for pre-coating, 2 is a nozzle for coating a magnetic layer for post-coating, 3 is a non-magnetic base film, and 4 is a magnetic paint. In the figure, the arrow indicates the running direction of the base film. The coating speed is about 100m / min,
Then, it was dried and cured to obtain a coating film of (Example 1).

FIG. 2 shows a sectional view of a magnetic recording medium according to an embodiment of the present invention. In the figure, 5 is a pre-coated magnetic layer, 6 is a post-coated magnetic layer, 3 is a non-magnetic base film (polyethylene terephthalate, polyethylene-2-6-naphthalate, etc.), and 8 is a back coat layer.
In Example 1, the pre-coating layer was 2.0 μm and the post-coating magnetic layer was 0.5 μm. Here, if the film thickness of the post-coating magnetic layer is less than 0.3 μm, it becomes difficult to form a uniform film thickness, and it becomes difficult to secure good medium surface properties, and contact with the magnetic head during recording / reproduction is made difficult. It becomes worse and recording and reproduction cannot be performed practically.

In addition, in the constitution of two magnetic layers, when the film thickness of the post-coating magnetic layer is larger than 1.0 μm, the flow-accelerating effect of the pre-coating magnetic layer of the pre-coating magnetic layer and the effect as the buffer layer act. Does not occur and the surface property of the medium is impaired. Therefore, the film thickness of the magnetic layer after coating is 0.3μ.
It was set to m to 1.0 μm.

(Example 2) In Example 2, a magnetic paint was prepared in the same format as in Example 1 except that the viscosity of the pre-coated magnetic paint used in Example 1 was further reduced by 5 poise. Was prepared. At this time, one double nozzle die nozzle coater as shown in FIG. 3 was used for coating the magnetic layer, and the thickness of the coating film was 2.0 μm for the pre-coated magnetic layer.
m, and the magnetic layer after coating was 0.5 μm to obtain a coating film of (Example 2). In the figure, 4 indicates a magnetic coating material, 9 indicates a double nozzle type coating nozzle, 3 indicates a non-magnetic base film, and arrows indicate the traveling direction of the base film.

(Example 3) Among the magnetic paints used in (Example 1), Mc type barium ferrite in which a part of iron element was replaced with a combination of tin element and magnesium element with Hc = 920 Oe as magnetic powder. The coating film of (Example 3) was prepared in the same manner as in (Example 1) except that the above was applied.

(Example 4) Among the magnetic paints used in Example 2, as magnetic powder, Hc = 920 Oe and M type barium ferrite in which a part of iron element was replaced with a combination of tin element and magnesium element. A coating film of (Example 4) was prepared in the same manner as in (Example 2) except for the above.

(Comparative Example 1) Using the same magnetic coating material as used in (Example 1),
After mixing and dispersing, a predetermined amount of lubricant and curing agent were added with stirring, and the magnetic coating was applied onto the non-magnetic film surface using a die coater at a coating speed of about 100 m / min. Then, a magnetic coating film was prepared by passing through a gap between oriented magnets having a magnetic flux in the same direction as the traveling substrate and drying and curing, to obtain (Comparative Example 1).

(Comparative Example 2) The magnetic coating material used in the magnetic layer of (Example 2) was mixed and dispersed, and a predetermined amount of a lubricant and a curing agent were added with stirring, and then the nonmagnetic film surface was coated. Using two gravure roll coaters with the above-mentioned magnetic paints arranged at intervals, a coating speed of about 100m / min was applied, and the magnetic paints were passed through the gap between the oriented magnets having a magnetic flux in the same direction as the running substrate and dried. Cure
A coating film having a thickness of 2.5 μm was produced, and (Comparative Example 2) was obtained.

(Comparative Example 3) The magnetic coating material used in the pre-coated magnetic layer of (Example 2) and the magnetic coating material used in the post-coated magnetic layer of (Example 1) were mixed and dispersed to give a predetermined amount. After stirring and adding the lubricant and the curing agent, the coating speed was set to about 100 m / min using a gravure roll coater and a die nozzle coater with the magnetic paint placed at intervals on the non-magnetic film surface. Was applied, passed through a gap between oriented magnets having a magnetic flux in the same direction as the traveling substrate, and dried and cured to prepare a coating film having a film thickness of 2.5 μm, and Comparative Example 3 was obtained.

(Comparative Example 4) The magnetic coating material used in the post-coating magnetic layer of Example 2 was mixed and dispersed, and a predetermined amount of a lubricant and a curing agent were added with stirring, and then the non-magnetic film surface was coated. 1. The magnetic coating material was applied using a gravure roll coater at a coating speed of about 100 m / min, passed through a gap between oriented magnets having a magnetic flux in the same direction as the traveling substrate, dried and cured to a film thickness of 2. A 5 μm coating film was prepared to obtain (Comparative Example 4).

The magnetic recording medium obtained as described above was slit to a 1/2 inch width, the medium surface roughness was measured by a non-contact type surface roughness measuring device, and a modified SVHS was used.
The electromagnetic conversion characteristics were measured using the deck. Electromagnetic conversion characteristics, equipped with a metal-in-gap type superstructure nitride film head with a gap length of 0.21 μm and a track width of 10 μm,
The relative speed between the tape and the head was measured and evaluated at 5.8 m / sec. Especially, regarding the electromagnetic conversion characteristics, the recording frequency is 12 MHz.
The RF output value and C / N value at z were measured. The measurement results are shown in (Table 1), and the frequency characteristics are shown as relative values with (Comparative Example 1) being 0 dB.

[0028]

[Table 1]

In (Example 1) to (Example 4), the surface roughness of the medium was improved by using the magnetic coating material having the same properties for the pre-coated magnetic layer and by using the coating method disclosed in the present invention. Compared with the case of a single-layer medium made of one magnetic paint, it has become possible to improve it significantly. As a result, as shown in (Table 1), in the high frequency region, that is, in the short wavelength region, the output is higher than that of the comparative example, and the characteristics of the coated barium ferrite medium obtained by the manufacturing method disclosed in the present invention are improved. The effect was clear, and the interlayer inconsistency between the two paints could be eliminated, and the strength of the medium could be improved, which could not be realized by the single-layering with one paint. When the film thickness of the post-coating magnetic layer is 0.3 μm or less, the fluidity of the coating material is improved, but the surface roughness of the pre-coating magnetic layer is reflected in the final surface property of the medium. Tape noise during movement becomes high. further,
When the film thickness of the post-coating magnetic layer was 1.0 μm or more, the effect of layering the same coating material was no longer exhibited.

As can be seen from the above results, in the examples using the present invention, the surface properties of the medium are further improved and the output in the short wavelength region is improved as compared with the samples of the comparative examples not using the examples. It became feasible. Here, the orientation mode is not limited in any way, and anisotropy may be imparted to the magnetic layer as a whole in the in-plane longitudinal direction or in the medium thickness direction, and between the pre-coated magnetic layer and the post-coated magnetic layer. You can change the anisotropy with. Although the tape-shaped coating film has been described in this embodiment, it is needless to say that the same effect can be obtained in the case of a disk-shaped, that is, a floppy disk.

[0031]

As described above, according to the present invention, the reproduction output in the short wavelength region can be achieved at a high level which could not be achieved by the prior art by making good use of the magnetic coating material having the same medium constitution and properties. A magnetic recording medium to be realized can be obtained. Therefore, a magnetic recording medium suitable for higher density recording can be provided, which is a very useful invention.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a coated portion of a method for manufacturing a magnetic recording medium according to an embodiment of the present invention.

FIG. 2 is a sectional view of a magnetic recording medium according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a coated portion of a method of manufacturing a magnetic recording medium according to another embodiment of the present invention.

[Explanation of symbols]

 1 Pre-coated magnetic layer coating nozzle 2 Post-coated magnetic layer coating nozzle 3 Non-magnetic base film 4 Magnetic coating 5 Pre-coated magnetic layer 6 Post-coated magnetic layer 7 Path roll 8 Back coat layer 9 Double nozzle type coating nozzle

Claims (4)

[Claims] 1. A magnetic recording medium in which a plurality of magnetic layers containing hexagonal ferrite plate-like magnetic powder and a resin binder are multilayer-coated on one surface of a non-magnetic base film. A magnetic recording medium, which is obtained by simultaneous multi-layer coating using two coating nozzles, each having the same layer in the wet state, separately provided in a wet state. 2. A magnetic recording medium in which a plurality of magnetic layers containing hexagonal ferrite plate-like magnetic powder and a resin binder are multi-layered on one surface of a non-magnetic base film. A magnetic coating material having the same layer, which is obtained by simultaneous multi-layer coating in a wet state using two coating nozzles separately provided, and then immediately subjecting it to magnetic field orientation so as to have an easy axis of magnetization in a certain direction. Item 1. The magnetic recording medium according to item 1. 3. The hexagonal ferrite plate-shaped magnetic powder comprises part of M-type barium ferrite or trivalent iron element.
The magnetic recording medium according to claim 1, which is barium ferrite magnetic powder substituted with a combination of a valent and a tetravalent metal element. 4. A magnetic recording medium in which a plurality of magnetic layers containing hexagonal ferrite plate-like magnetic powder and a resin binder are multi-layered on one side of a non-magnetic base film, and the plurality of magnetic layers are provided. A method for producing a magnetic recording medium, comprising performing simultaneous multilayer coating by using two coating nozzles separately provided in a wet state with magnetic coatings having the same layer.